The present invention relates to a clad-type brazing filler for use in bonding ceramics either to themselves or to metals or glass (In the discussion below, reference is primarily made to the bonding of metals to ceramics, but it is to be understood that the invention applies as well to the bonding of any of these materials to ceramics.) The invention also relates to a composite prepared by using such a filler.
Ceramics are conventionally bonded to metals either by a high-melting method or by an oxide solder method. According to the first method, an alumina ceramic is bonded to Kovar by the following procedure: sintered alumina ceramic with a Mo-Mn paste coat is baked in a hydrogen furnace at 1,300.degree. to 1,700.degree. C.; the ceramic is plated with a nickel deposit on the Mo-Mn coat and heated in a hydrogen furnace at about 800.degree. C. to form a metallized Ni layer; and the alumina ceramic having the Ni and Mo-Mn coats is bonded to Kovar by a silver-copper eutectic brazing filler. According to the oxide solder method, an alumina ceramic is bonded to niobium by the following procedure: a mixture of CaO, MgO, Al.sub.2 O.sub.3 and B.sub.2 O.sub.3 is coated onto a sintered alumina ceramic, and after forming thereon a layer of metallic niobium, the ceramic is heated at about 1,500.degree. C. at a reduced pressure of 10.sup.-5 Torr.
However, both methods are only applicable to the bonding of articles whose coefficients of thermal expansion are close to each other. In addition, the high-melting metal method is complicated, whereas the oxide solder method, which requires the use of a vacuum, is not highly adapted to efficient bonding operations.
Nonoxide ceramics can be bonded to metals by a method which consists of first metallizing the ceramic either by metal vapor deposition or by a copper sulfate method, and then brazing the metallized surface of the ceramic to the mating metal. However, this method is disadvantageous in that heating is necessary for each of the two separate metallizing and brazing steps.